Last year chemist James Tour made graphene quantum dots from coal. Now his team has combined the dots with tiny sheets of graphene.

The result is a hybrid material that could make it much cheaper to generate energy with fuel cells.

The lab discovered boiling down a solution of graphene quantum dots (GQDs) and graphene oxide sheets (exfoliated from common graphite) yielded self-assembling nanoscale platelets that could then be treated with nitrogen and boron.

A typical nanoplatelet as seen under an electron microscope. (Credit: Tour Group/Rice University)This image shows the rough surface of a graphene quantum dot/graphene nanoplatelet before modification with nitrogen and boron. (Credit: Tour Group/Rice University)

[related]

The hybrid material combined the advantages of each component: an abundance of edges where chemical reactions take place and excellent conductivity between GQDs provided by the graphene base. The boron and nitrogen collectively add more catalytically active sites to the material than either element would add alone.

“The GQDs add to the system an enormous amount of edge, which permits the chemistry of oxygen reduction, one of the two needed reactions for operation in a fuel cell,” Tour says. “The graphene provides the conductive matrix required. So it’s a superb hybridization.”

The material outperformed commercial platinum/carbon hybrids commonly found in fuel cells. The material showed an oxygen reduction reaction of about 15 millivolts more in positive onset potential–the start of the reaction–and 70 percent larger current density than platinum-based catalysts.

The materials required to make the flake-like hybrids are much cheaper, too, Tour says.

“The efficiency is better than platinum in terms of oxygen reduction, permitting one to sidestep the most prohibitive hurdle in fuel-cell generation—the cost of the precious metal,” he adds.